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我在使用用于将文件下载到调用 HTTPHandler.ashx 文件的网络方法时遇到问题。处理程序调用 web 方法如下：

byte[] docContent;
string fileType;
string fileName;
string msgInfo = brokerService.DownloadFile(trimURL, recNumber, out docContent, out fileType, out fileName);

在被调用的 web 方法中，我必须在使用它之前初始化字节数组，否则我会在所有返回语句上得到编译器错误：

The out parameter 'docContents' must be assigned to before control leaves the current method

我尝试将其设置为一个空数组，但这会导致 Buffer.BlockCopy 方法失败：

Offset and length were out of bounds for the array or count is greater than the number of elements from index to the end of the source collection.
mscorlib
  at System.Buffer.BlockCopy(Array src, Int32 srcOffset, Array dst, Int32 dstOffset, Int32 count)

我知道我需要初始化它，但在访问数据库之前我不知道所需的数组长度。通过调试，我验证了除 Buffer.BlockCopy 之外的所有代码都可以正常工作：

    public string DownloadFile(string trimURL
        , string TrimRecordNumber
        , out byte[] docContents
        , out string returnFiletype
        , out string returnFilename)
    {
        docContents = new byte[0];
        returnFiletype = null; returnFilename = null;
        try
        {
            ConnectToTrim(trimURL);
            if (!db.IsValid)
                return "CRITICAL: Database Is NOT Valid";
            Record myRec = db.GetRecord(TrimRecordNumber);
            if (myRec == null)
                return "CRITICAL: Record not found.";
            uint bufferSize = 10000;
            int documentLength = myRec.DocumentSize;
            byte[] result = new byte[documentLength];
            byte[] buffer = new byte[bufferSize];
            uint bytesRead;
            uint totalBytesRead = 0;
            TRIMSDK.IStream docStream = myRec.GetDocumentStream(string.Empty, false, string.Empty);
            while (totalBytesRead < documentLength)
            {
                docStream.RemoteRead(out buffer[0], 10000, out bytesRead);
                for (int i = 0; i < bytesRead; i++)
                {
                    result[totalBytesRead] = buffer[i];
                    totalBytesRead += 1;
                }
            }
            returnFiletype = myRec.Extension;
            returnFilename = myRec.SuggestedFileName;
            Buffer.BlockCopy(result, 0, docContents, 0, result.Length); 
            return string.Format("OK-Document for recordnumber({0}): {1}.{2} - size: {3} bytes",
                TrimRecordNumber, returnFilename, returnFiletype, Convert.ToString(documentLength)); 
        }
        catch (Exception ex)
        {
            return LogException(ex, "CRITICAL: Exception in DownloadFile method has been logged:", trimURL, 100);
        } 
    }
4

1 回答 1

5

您可以从将其初始化为 null 开始。就在调用之前Buffer.BlockCopy，分配并初始化它到适当的长度。

这看起来像：

public string DownloadFile(string trimURL
    , string TrimRecordNumber
    , out byte[] docContents
    , out string returnFiletype
    , out string returnFilename)
{
    docContents = null;

    //...

        returnFiletype = myRec.Extension;
        returnFilename = myRec.SuggestedFileName;
        docContents = new byte[result.Length]; // Allocate appropriately here...
        Buffer.BlockCopy(result, 0, docContents, 0, result.Length); 
        return ...

或者，您可以直接将结果分配并复制到其中-完全docContents不需要。但是，如果您想单独保留整体流量控制，result您仍然需要在开始时进行初始化。null

于 2011-08-30T20:00:01.487 回答